If you haven’t already look through these , you might find something you fancy in herehttp://themeforest.net/browse/tags/default/horizontal
I have a new post on notes that talks about inspiring Facebook cover picshttp://notes.envato.com/inspirations/inspiring-cover-photos-for-your-facebook-timeline/
I would love to know if you guys have come across some other interesting cover pics that inspired you.
I also would like to do a twitter and G+ post about these soon so feel free to drop those in here too.
I use WPEngine, they are pretty good from what I can see so far. They are quick to respond to support tickets.
no experience with MT but was not a big fan of goDaddy hosting ( used to run with them a couple of years ago )
as for CDN and caching WPEngine has their own solution .. they only allow WordPress on their server and so I assume you are after a caching solution for WordPress ( try http://wordpress.org/plugins/w3-total-cache/ , you can hook it up with a CDN like Amazon Cloudfront, MaxCDN, Akamai or Rackspace Cloud Files ).
Hope this helps